Many All Terrain Vehicles (ATVs) and snowmobiles are equipped with belt-driven continuously variable transmissions. Continuously Variable Transmissions (CVTs) alleviate the need for the operator of the vehicle to shift the transmission as the vehicle accelerates through its range of speeds. As described in U.S. Pat. No. 6,176,796, CVTs are comprised of a drive clutch, a driven clutch, and drive belt, typically a V-belt, disposed about the clutches. The drive clutch is coupled to the engine drive shaft and the driven clutch is coupled to the vehicle's wheels on ATVs or endless track in the case of snowmobiles and is driven by the drive clutch though the drive belt. Each of the clutches are typically configured as a pair of opposed sheaves that rotate together about a common axis. Typically one sheave of each clutch is moveable axially while the other remains stationary. The movable sheaves thus move away from or towards the other sheave during operation of the vehicle.
The drive belt slides radially inward and outward along the inner faces of the sheaves during operation. The inner faces of the sheaves are angled such that they converge towards a center axis. In operation, as the axial distance between the sheaves increases, the drive belt moves inward toward the axis of rotation. Conversely, as the axial distance decreases, the drive belt moves outward toward the outer radius of the clutch. The sliding of the belt results from frictional forces. This friction creates a significant amount of heat. If this heat is not adequately removed from the sheaves, the belt can become quite hot and, under extreme conditions, the belt will burn, warp or fray and thereby fail or operate improperly.
Drive belts are more apt to fail under certain vehicle operating conditions. For example, the drive belt may be driven by the drive clutch yet spin or slide without moving the driven clutch. This conditions can occur when an operator applies full throttle even though the wheels on the vehicle are stuck or when the vehicle is towing a very heavy load. The increased throttle results in rotation of the drive clutch but the stuck wheels or the heavy load prevents rotation of the driven clutch. The drive belt absorbs the large difference in speeds by sliding relative to the stationary clutch which generates significant amount of heat that may result in belt failure.
Another scenario in which the drive belt is more apt to fail is if the vehicle is driven in the wrong gear. In addition to the CVT, ATVs often have a second type transmission consisting of traditional gears. The second transmission is usually located on the driven side of the CVT and may be shifted between High, Low, Reverse and Neutral. If the vehicle is mistakenly operated in High gear when conditions warrant Low gear operation, the load on the engine and on the CVT drive clutch increases. This increased load causes the drive belt to slip on the driven clutch resulting in extreme heat generation.
Thus it is desirable to provide a system and method of alerting an operator whenever the immediate operating conditions of the vehicle make a drive belt more prone to burning so that the operator can take preventative action.